OxyContin 20mg BID to MSER Conversion
OxyContin 20mg twice daily (40mg total daily) converts to approximately 60mg of Morphine Sulfate Extended Release (MSER) per day, typically administered as 30mg twice daily.
Calculation Method
The conversion is based on the established opioid equivalency ratio between oxycodone and morphine:
- Total daily oxycodone dose: 20mg × 2 = 40mg/day 1
- Conversion factor: Oxycodone has a conversion factor of 1.5 to morphine milligram equivalents (MME) 1, 2
- Calculation: 40mg oxycodone × 1.5 = 60 MME (morphine equivalents) per day 1, 2
Recommended MSER Dosing
- Total daily MSER dose: 60mg/day 1, 2
- Typical administration: 30mg MSER twice daily (BID) to match the extended-release profile 1
- Alternative: Some clinicians may use 20mg three times daily, though BID dosing better matches the original OxyContin schedule 1
Critical Safety Considerations
Dose reduction is strongly recommended when converting between opioids to account for incomplete cross-tolerance and individual pharmacokinetic variability 1, 3:
- Reduce the calculated equianalgesic dose by 25-50% when switching opioids 1, 3
- This would suggest starting with 30-45mg MSER daily (15-22.5mg BID) rather than the full 60mg 1
- Titrate upward based on pain control and tolerability 1, 3
Important Caveats
The 1.5 conversion factor is widely accepted but shows some variation in clinical practice 1:
- Some sources cite oxycodone potency as 1.5-2 times that of morphine 1, 4
- The CDC guideline uses 1.5 as the standard conversion factor 1
- NCCN cancer pain guidelines also support the 1.5-2 range 1
Equianalgesic conversions are estimates only and cannot account for individual differences in genetics, metabolism, and prior opioid exposure 1, 3, 5:
- Significant variability exists between clinicians in opioid conversion practices 5
- Monitor closely for signs of inadequate pain control or opioid toxicity after conversion 3
- Provide immediate-release morphine for breakthrough pain during the transition period 1
Practical Implementation
For a conservative approach in clinical practice:
- Start with 45mg MSER daily (22.5mg BID, rounded to available tablet strengths) 1
- Provide immediate-release morphine 10-15mg every 4 hours as needed for breakthrough pain 1
- Reassess within 24-48 hours and adjust based on breakthrough medication requirements 1
- If patient required minimal breakthrough doses and pain was well-controlled on OxyContin, the full 60mg MSER daily may be appropriate 1, 2